1. Technical Field
This invention relates to drilling fluids for use in various drilling methods and to novel lubricating drilling fluid compositions for use in widely varying drilling procedures. The invention is particularly concerned with non-polluting non-toxic biodegradable drilling fluids which are based on plant and vegetable oils and are applicable to emulsified addition to water to form natural water in oil based drilling fluids having improved lubricating characteristics under both high and low load and pressure conditions. The fluids are useful in both variable load and extreme operating conditions such as evidenced by changes in the drag of the drill pipe which occurs during drilling in severe conditions, during vertical movement of the drill pipe into and out of the drill hole such as to change the drill bit, increases in bit balling, and increases in the tendency of the drill pipe to become stuck. The fluids are natural oil based and exhibit non-toxicity toward aquatic life and possess valuable rheological properties as disclosed hereinafter.
2. Prior Art
In the drilling of wells to recover hydrocarbons such as oil and/or gas from subterranean deposits, it is common practice to use a rotary drilling procedure in which a drill bit is rotated at the bottom of the bore hole by means of rotating hollow drill pipe which extends to the surface. The drill pipe is driven from the surface and a circulating fluid commonly referred to as a drilling fluid or drilling mud is pumped through the drill pipe where it emerges through openings in the drill bit to cool the same and is returned to the surface in the annular space between the drill pipe and the walls of the bore hole.
The drilling fluid, upon emerging from the well at the surface, may be mechanically processed to remove the cuttings and other undesirable contaminants and is normally treated chemically to maintain certain chemical and physical properties of the fluid depending upon particular drilling conditions encountered. The drilling fluid after being reconstituted is normally recirculated by pumps to be forced downwardly through the drill pipe, this circulaton being generally continuous during drilling. Circulation of the drilling fluid may be interrupted occasionally such as when an additional section of drill pipe is added at the top of the string of pipe or when the entire length of drill pipe is withdrawn to replace or repair the drill bit.
The drilling fluid must be capable of performing many varied functions which are required in a successful drilling procedure and therefore must possess certain desirable chemical and physical properties. The drilling fluid must have sufficient viscosity to suspend and remove the cuttings from the bore hole and must have sufficient gel strength to hold solids in suspension, especially when circulation of the fluid is interrupted. It also must have sufficient density to exert suitable pressure to the sides of the bore hole to prevent the entrance of fluids into the bore hole from the earth formation being penetrated, and it must have low fluid loss to prevent undue loss of fluid into the formation by its deposition on the bore hole sides such as by forming an impervious filter cake or deposit. Further, it must lubricate both the bearing and cutting surfaces of the drill bit as well as the string of drill pipe both upon rotation and vertical movement. Frequently, in the drilling of wells and especially in directional drilling, the friction between the string of drill pipe and the sides of the bore hole may be sufficient to interfere with vertical movement of the pipe into and out of the hole. Such high friction between the drill pipe and the bore hole increases power required to rotate the drill pipe and the increased torque causes wear and stress on the pipe thus decreasing the drilling rate and causing the possibility of pipe twist-off or breakage.
The lubrication characteristics of drilling fluids have been the subject of many investigations, most prior art patents disclosing different types of additives for use in petroleum oil base drilling fluids, water-in-oil emulsion drilling fluids, and water base drilling fluids. Also, it has been proposed to incorporate an emulsifier in water base drilling fluids where the lubricating additive is insoluble in water. Many of the prior art additives function as extreme pressure lubricants and are added to the drilling fluid primarily to lubricate the bearings of the drill bit. Some of the known prior art additives also serve to impart sufficient lubricity to the drilling fluid to decrease the power required to rotate the drill pipe by reducing the drill string torque. These additives serve to decrease the friction occurring between the drill string and the sides of the bore hole thus increasing the lubricity of the drilling fluid.
Many of the in oil type drilling fluids having lubricating characteristics have been based upon mineral oils or diesel oil with the addition of additives therein to effect an emulsion. Pollution and toxic features of such materials are becoming increasingly objectional which limit their effectiveness. Also, some of the prior art additives are not effective at a pH above about 10.5 and others are not effective in the presence of calcium or other polyvalent cations. In addition, certain of the additives are absorbed onto the surface of the solids present in or carried by the drilling fluid which may deactivate the additive and may cause oil wetting of the solids resulting in fluctuation and settling, especially if barite is present as the weighting material. Certain additives cause the drilling fluid to foam while others are difficult to disperse in the drilling fluid. Others cause the drilling fluid to fluoresce under ultraviolet light which interferes with certain well logging operations performed to indicate the presence of oil in the earth formations being penetrated. Also, some of the additives must be employed in such great concentrations to be ineffective from the standpoint of economics.
As is known in current practice, drilling muds based on diesel fuel oil and the like have been the primary medium for providing lubricants to the drill pipe in drilling for hydrocarbons. One major disadvantage in using such materials has been in drilling offshore and in lakes or wetlands, their polluting characteristics having caused severe logistics problems. Such diesel fuel based fluids cannot be disposed of in the ocean or lakes due to environmental and pollution concerns and their adverse effect on aquatic life. In such cases the diesel fuel containing fluids must be transported ashore to a suitable type of disposal or recovery system. Increasingly stringent regulation of the adverse environmental effects of diesel oil in drilling fluids requires the development of non-polluting replacements. Pollution has usually been defined as a sheen, film or discoloration of surface water adjoining shorelines such as formed by petroleum-based oils and is prohibited.
U.S. Pat. Nos. 2,222,949, 2,316,967, 2,316,968 and 2,698,833 primarily relate to oil-base, non-aqueous drilling fluids all of which are inherently polluting. U.S. Pat. No. 2,698,833 is directed to a drilling fluid which is prepared with a thermally stable oil having less than about 5% aromatics and unsaturates by volume to be non-fluorescing. However, it still possesses objectionable polluting properties.
U.S. Pat. No. 3,761,410 discloses water based drilling fluid with increased lubricity, the water being dispersed as discreet small non-emulsified droplets in the fluid. This composition includes water insoluble alkyl alcohol, a lubricating additive consisting of a vegetable oil or tall oil and a pour point depressant consisting of an alcohol or glycol.
U.S. Pat. No. 4,374,737 disloses a drilling mud composition for mixing with water which comprises major amounts of diethanolamine, tall oil fatty acid and imidazoline/amide mixture with a biodegradable non-polluting vegetable oil comprising a minor amount of the composition, the latter to act as an emulsifier when the composition is added to water. These fluids are described as not requiring additional emulsifiers to maintain the emulsion and possessing desired rheological properties comparable to those obtained with crude or diesel oil; however, they do require major amounts of the concentrate.